1. Field of Invention
The present invention relates to a field of high frequency, high power and small-sized vacuum electronic devices mainly applied but not limited to high power and small-sized Terahertz radiation sources and Cherenkov particle detectors and emitters based on reversed Cherenkov radiation effect.
2. Description of Related Arts
Terahertz radiation comprises coherent electromagnetic radiation roughly in a range from 0.1 to 10 THz and narrowly in a range from 0.3 to 3 THz between the short-wavelength edge of microwave band and the long-wavelength edge of far-infrared light. Terahertz technology causes an extensive research boom around the world. This is because Terahertz electromagnetic wave has many novel electromagnetic features and potential applications. First of all, Terahertz radiation has stronger penetrativity than infrared light and visible light and is able to penetrate cloth, plastic and others with little attenuation, so the Terahertz radiation can be applied in aspects of safety surveillance, radar and communications. Secondly, the Terahertz radiation has photon energy far lower than X ray, and thus the Terahertz radiation does no big harm to organism tissues and DNA molecules and can be applied in biomedicine fields including DNA detection, genetic analysis and tomographic imaging. Thirdly, Terahertz spectrum is able to carry much information about a compound, including biochemical constituents and spectrum features, and plays an extremely important role in biochemistry and other fields. However, a lack of high power Terahertz radiation sources hinders the Terahertz technology from being realized in many of the above fields.
Metamaterials are artificially structured materials with unusual electromagnetic properties that are not found in natural materials. One of the metamaterials is Double-Negative Metamaterial (DNM) whose effective permittivity and permeability both have negative real parts. The DNM has some novel electromagnetic features, such as negative refractive index, reversed Cherenkov radiation, reversed Doppler effect, reversed refraction law and so on. A realization of the DNM is rated by the American magazine, Science, as one of the top ten technological breakthroughs of 2003 because of promising theoretical values and wide application prospects thereof; the “invisible cloak” made of the metamaterials is also rated by Science as one of the ten technological breakthroughs of that year in 2006; and the metamaterials are rated by Science as one of the insights of the Decade in 2010.
An article of {hacek over (C)}erenkov radiation in materials with negative permittivity and permeability (Opt. Express, 11, 723, 2003) written by J. Lu et al from MIT introduces reversed Cherenkov radiation effect generated by a single charged particle passing through infinitely large isotropic DNM, wherein the authors made thorough researches respectively about the reversed Cherenkov radiation under conditions of loss and dispersion. In an article of Cherenkov radiation by an electron bunch that moves in a vacuum above a left-handed material (Phys. Rev. B, 72, 205110, 2005), Y. O. Averkov et al theoretically studied Cherenkov radiation by an electron bunch that moves in a vacuum above an isotropic DNM and results thereof show that the Cherenkov radiation in the isotropic DNM has “reversed” features. S. N. Galyamin et al theoretically analyzed reversed Cherenkov radiation and transition radiation generated by a single charged particle crossing through a DNM boundary in an article of Reversed Cherenkov-Transition Radiation by a Charge Crossing a Left-handed Medium Boundary (Phys. Rev. Lett., 103, 194802, 2009). Z. Y. Duan et al thoroughly studied about reversed Cherenkov radiation in a circular waveguide fully or partially filled with DNM and effective methods for enhancing the radiation in articles including Reversed Cherenkov radiation in a waveguide filled with anisotropic double-negative metamaterials (J. Appl. Phys., 104, 063303, 2008), Cherenkov radiation in anisotropic double-negative metamaterials (Opt. Express, 16, 18479, 2008) and Enhanced reversed Cherenkov radiation in a waveguide with double-negative metamaterials (Opt. Express, 19, 13825, 2011), wherein the conventional electromagnetic radiation has potential applications to Cherenkov particle detectors and emitters and high frequency, high power electromagnetic radiation sources. In an American patent Smith-Purcell radiation source using negative-index metamaterial (U.S. Pat. No. 7,397,055 B2 July 2008), D. L. Barker et al disclosed periodic grating structure formed by Negative Index Metamaterials (NIMs) as shown in FIG. 1, by which Smith-Purcell radiation is enhanced when an electron beam moves close to a surface of the grating structure compared to the normal metal gratings case. In a latest article of Novel electromagnetic radiation in a semi-infinite space filled with a double-negative metamaterial (Phys. Plasmas, 19, 013112, 2012) written by Z. Y. Duan et al, the authors proved that when a single charged particle moves in a vacuum close to an interface between isotropic DNM and vacuum, reversed Cherenkov radiation is formed in the DNM as shown in FIG. 2 and surface wave (SW) amplitude in vacuum is obviously enhanced compared to normal dielectric materials case, as shown in FIG. 3; the authors put forward a Chinese patent application on May 27, 2011 (application number: 201110139754.1; isotropic Double-Negative artificial Metamaterials; inventors: Z. Y. Duan, C. Guo, T. Tang; status: being processed).